Swiss banks have "allegedly" begun providing information to Washington on accounts held by US citizens, Swiss media reported on Saturday.
Local daily Neue Zuercher Zeitung reported that US authorities had "allegedly" received information from Swiss banks on their American customers, without citing sources.
It said that yesterday nine banks "allegedly ... provided the requested information".
Another media outlet, the daily TagesAnzeiger, said that Credit Suisse had earlier in the week provided to Washington information on US clients.
"The Credit Suisse banker responsible for the negotiations took a plane for Washington and submitted the information," it said.
The TagesAnzeiger also said that Switzerland's government has "partially" agreed to a Washington ultimatum that information on US nationals who have money in the country be handed over.
It said that Swiss authorities, in a confidential letter to 10 local banks said the US request could "be partially agreed upon", but that the data transfer would have to be done by the banks themselves, and not the government.
Furthermore, the letter said the banks would need to provide data on banking activities only going back to September 30, 2009.
Prior to that date, information should only be provided "if there is a violation of US legislation or obvious tax fraud", the newspaper said.
On Wednesday, Switzerland's President Micheline Calmy-Rey told reporters that Swiss authorities had not provided the names of any clients of Swiss banks to US tax authorities.